For the condenser microphone, an electrostatic acoustic-electric converter provided in a microphone unit has a very high impedance. Therefore, the microphone incorporates an electronic circuit for producing a sound signal including an impedance converter. As the impedance converter, a field effect transistor (FET) has usually been used.
The electronic circuit is accommodated in a shielded space formed by a metallic microphone casing. If the shield is incomplete, a high-frequency current caused by external electromagnetic waves (especially, strong electromagnetic waves emitted from a cellular phone) flows into the microphone casing, and is detected by the impedance converter, whereby noise of an audible frequency may be generated.
In particular, for a microphone of a type such that a microphone cable is directly drawn into the microphone casing, such as a tie clip microphone or a gooseneck microphone, the shield in a microphone cable draw-in portion becomes incomplete easily (for example, refer to Japanese Patent Application Publication No. 2006-128850).
On the other hand, for the microphone of the type such that the microphone cable is directly drawn into the microphone casing, as measures against a pulling external force applied to the microphone cable, as described, for example, in Japanese Patent Application Publication No. 2006-19854, a knot of microphone cable is generally formed in the microphone casing.
However, the above-described measures are not favorable as the measures against external electromagnetic waves because the formation of the knot increases the wiring length of the microphone cable in the microphone casing.
An object of the present invention is to provide a condenser microphone of a type such that a microphone cable is directly drawn into a microphone casing, in which the electromagnetic shieldability of a microphone cable draw-in portion can be enhanced, and the microphone cable can be fixed easily.